the two ortho films differ in price and quality.
While the economically priced display film is like a photopaper on a clear base, the ORTHO CT is actually a high resolution technical film but with a normal grade as opposed to most other technical films which feature an increased contrast.
So ideally you would use the CT for any type of negative contacting and the Display film to make enlargements onto.
Whether the ortho CT gives you superial results over the display film depends on the enlargement factor and grain of the original negative.
If you want to enlarge a 35mm negative of a medium or high speed film to 16x20 Inch the display film will give you probably as satisfying a result as the ORTHO CT would.
If we are talking 4x5" 25 ASA film enlarged to 8x10" I would take the CT film.